Not entirely sure why this would happen suddenly.
The build failed half-way through so I restarted the build. It could have uploaded some broken files, but the signature should be valid.
Assuming the network is otherwise working fine, it seems to indicate that the updater URL is broken. I hope this is not a broken beta build …
Could you try running Duplicati.Library.AutoUpdater.exe and see what URLs it reports using?
That does indicate some problems with IE not supporting the JS features. Unfortunately we only have automated testing with FF (which is currently failed for other reasons).